Presently, in order to fabricate semiconductor devices with a fast operating speed and high reliability, a metal of copper is used as a metal line material because it has a low resistivity and high resistance against electrical movement or stress compared with a conventional metal of aluminum (Al).
However, a copper metal line is difficult to be etched by an existing dry etch method. Thus, the copper metal line is generally patterned by a single damascene method or a dual damascene method.
The damascene method refers to a method of forming a pattern of a metal line or a contact hole in an interlayer insulating layer for insulating between metal lines, depositing a metal layer and then removing the metal layer by a conventional method, such as Chemical Mechanical Polishing (CMP), thereby forming the metal lines.
The dual damascene method refers to a method of patterning both a metal line and a contact hole in an interlayer insulating layer, filling the patterned portion with a metal layer for the metal line, and removing an unnecessary portion of the metal layer. Due to the advantages of a simplified process and cost effectiveness, the dual damascene method is being widely used as a method of formatting the metal line.
Further, copper has a low adhesive force as compared to a silicon oxide (SiO2). Also, copper has a diffusion coefficient greater, e.g., about 100 times than that of aluminum (Al) within silicon (Si). Thus, in order to secure the reliability of a semiconductor device, there is a need for an anti-diffusion film capable of preventing diffusion while having good adhesiveness with an insulating film.
As far as the anti-diffusion film is concerned, titanium nitride (TiN) is generally used as barrier metal at the sidewalls and bottom of the copper metal line. A silicon nitride (SiN) film is generally used as the insulating anti-diffusion film at the top surface of the copper metal line.
FIGS. 1a to 1d are a cross-sectional perspective view of a semiconductor substrate illustrating a method of forming a copper metal line according to a conventional dual damascene method.
As shown in FIG. 1a, an interlayer insulating layer 30 is deposited on a semiconductor substrate 10 in which a lower metal line 20 is formed. Photo/etch processes are performed to form a via contact hole 40 and a metal line pattern (or a trench) 50 over the semiconductor substrate.
Thereafter, a barrier metal film 60 and a copper seed layer (not shown) are deposited. The semiconductor substrate is processed by an electrochemical plating (ECP) method to form a copper layer 70 as shown in FIG. 1b. The semiconductor substrate over which the copper layer 70 is formed is processed by chemical mechanical polishing (CMP), so that the copper layer 70 and the barrier metal film 60 except for a portion of the metal line to be formed are sequentially removed to thereby form a copper metal line, as shown in FIG. 1c. 
Thereafter, while an insulating anti-diffusion film 80 is deposited, the processes as described above are repeated to form an upper copper metal line.
In the copper metal line formation process according to the conventional dual damascene method, a silicon nitride (SiN) film is generally used as the insulating anti-diffusion film of a copper metal. The SiN film is deposited on the copper metal line after a chemical mechanical polishing (CMP) process for the copper metal is performed as shown in FIG. 1d. However, since the copper metal and the SiN film have poor adhesion and form an unstable surface state, there are problems in that an electromigration (EM) characteristic is degraded and reliability is lowered.
In other words, as shown in FIGS. 2a and 2b, an unstable adhesive surface or an unstable surface state of the SiN film and the copper metal line causes to be provided as the migration path of copper atoms by electron wind, which results in forming a void such as a via void or a line void. In particular, in a downstream electron flow as shown in FIG. 2b, the unstable adhesive surface or the unstable surface state of the SiN film and the copper metal line leads to a line void. Accordingly, there is a problem in that the reliability of a semiconductor device is degraded.